Displays the best WALL TIME for execution of the given code. This
is based on the Python timeit module, which avoids a number of
common traps for measuring execution times. It is also based on
IPython’s %timeit command.

TYPICAL INPUT FORMAT:

timeit(statement, preparse=None, number=0, repeat=3, precision=3)

EXAMPLES:

sage: timeit('2^10000')625 loops, best of 3: ... per loop

We illustrate some options:

sage: timeit('2+2',precision=2,number=20,repeat=5)20 loops, best of 5: ... per loop

The preparser is on by default (if it is on), but the preparse option
allows us to override it:

sage: timeit('2^10000',preparse=False,number=50)50 loops, best of 3: ... per loop